Background: Widening of the tracheal bifurcation angle on chest radiograph is mentioned as a sign of left atrial (LA) enlargement. However, the clinical usefulness of this sign as a diagnostic tool remains controversial. The aims of our study were: 1) to determine the relationship between subcarinal angle and echo-measured LA volume, and 2) to assess the diagnostic value of measuring subcarinal angle for predicting LA enlargement.Methods: A total of 376 subjects who underwent echocardiography between September 2004 and June 2007 were enrolled in our study. LA volumes data were obtained, and then indexed by body surface areas. LA enlargement was defined as LA volume index (LAVI) > 28 ml/m^2. Subcarinal angles of each subject were calculated using their chest posterior-anterior view, and data were analyzed by statistical methods.Results: Application of Student's t-test disclosed subcarinal angles which were significantly greater in patients in the LA enlargement group than those outside the LA enlargement group (p = 0.0035). Furthermore, linear regression revealed a significant positive correlation between subcarinal angles and LAVI (r = 0.41, p < 0.001). However, ROC curve showed no optimal cut-off value of subcarinal angle which could predict LA enlargement.Conclusion: Our study demonstrated that the subcarinal angle measured by chest radiograph significantly correlated with echo-measured LA volume. However, there was no practical upper limit of "normal" subcarinal angle which was efficacious for detecting LA enlargement.